Low-temperature absorption refrigeration



F. E. GILMORE LOW-TEMPERATURE ABSORPTION REFRIGERATION Filed Aug. 22, 1947 Sept. 1 1953 g Sheets-Sheet 2 Lllalll Forr'zsf E.Gi|morz Patented Sept. 1, 1953 UNITED LOW-TEMPERATURE ABSORPTION REFRIGERATION Forrest E. Gilmore, Bartlesville, 0kla., assignor to Phillips Petroleum Company, a corporation of Delaware Application August 22, 1947, Serial No. 770,055

7 Claims.

This invention relates to apparatus and methods by means of which efficient low tem perature refrigeration is accomplished economically by means of multi-stage expansion and absorption using anhydrous ammonia as a refrigerant and aqua ammonia as the absorbent.

The general object of this invention is to provide a novel economical method and apparatus to effect efficient low temperature refrigeration employing an ammonia absorption system in a plurality of expansion and absorption stages.

Another object of this invention is to provide a refrigeration system and method of this type using a relatively small amount of power driven machinery, resulting in low operating and repair costs and eliminating mechanical hazards of other refrigeration systems such as the propane compression type of refrigeration system.

Another object of this invention is the use of an ammonia absorption refrigeration system wherein cooling is effected in stages in which the ammonia is successively evaporated at progressively lower pressures and the ammonia vapor generated is absorbed in the same aqua ammonia moving through the successive stages in the order of increasing pressures.

Other and more detailed objects of the invention will be apparent from the following disclosure of the several embodiments thereof illustrated in the attached drawings.

This invention resides substantially in the combination, construction, arrangement, relative location of parts, steps and series of steps, all as will be described in detail below.

In the accompanying drawings--.

Figure l is a schematic and diagrammatic illustration of one form of apparatus embodying the principles of this invention; and

Figure 2 is a similar illustration of the application of the principles of this invention to the extraction of natural gasoline from natural gas.

In the system of Figure 1 the supply of liquid refrigerant, preferably anhydrous ammonia,

, flows from the condenser of a still, not shown,

through the line I into the flash tank 2, the liquid level of which is determined by the fluid pressure operated valve 3 actuated as indicated by the liquid level controller 4. The system disclosed employs quite a few of these fluid pressure actuated valves and liquid level controllers. The valves are, as illustrated, of the diagram type available commercially in many forms and the liquid level controllers are likewise commercially known in several forms suitable for the purpose.

The valves 3 are actuated by and in accordance with changes in the liquid level which actuates the liquid level controller to in turn control the exhaust of pressure fluid to the motor valves to cause them to operate in the proper direction to maintain a predetermined liquid level.

The flash tank 2 is connected to the primary absorption cooler 5 by means of the liquid line 6 and the vapor line 1 which returns to the flash tank 2 above the maintained liquid level therein.

" The cooler 5 is a tube type of heat exchanger in which the tubes 8 are immersed in the liquid anhydrous ammonia and the material to be cooled flows through the tubes. Heat exchangers of this type are well known devices in this art.

The liquid absorbent in this case, preferably very weak aqua ammonia, is supplied from a still, not shown, through the line 9 to the heat exchanger 5 so as to be delivered to the tubes thereof. In the line 9 is a water cooler It! for cooling the aqua ammonia. After passing through the tubes of. the heat exchanger 5 the aqua ammonia is delivered by means of the line I2 into the uppermost section I l of the absorber generally indicated by the reference numeral l3. The aqua ammonia is discharged into the absorber through the line l2 at a desired temperature which temperature is controlled by the motor valve l4 and the thermostat 16. The valve i4 is in the line 15 coming from the top of the flask tank and controls the pressure on the liquid ammonia in the heat exchanger 5 and thus its temperature.

In section ll of the absorber l3 the cold absorbent, aqua ammonia, passes downwardly over a plurality of bubble trays H, or other form of baffling and is warmed as it absorbs refrigerant vapors and collects on the take-off tray l8. It is delivered from the take-off tray [8 through a line l9 to and through the secondary absorbent cooler or heat exchanger 20 which is like the heat exchanger 5. In the cooler 20, if extremely low temperatures are desired, the absorbent is cooled by evaporation of liquid refrigerant to a lower temperature than it was cooled in the primary cooler 5. From the secondary cooler 20 the secondary absorbent passes through line 2! back into the section I l of the absorber below the tray l8. Pipe [9 has a pump 22 and a motor valve 23 controlled by the liquid level device 24, as indi cated. This arrangement throttles the flow of partially saturated absorbent from the take-off tray l 8 so as to maintain a constant liquid level of the absorbent on the take-off tray I81.

The cold absorbent descends through the bubble tray ii in the lower part of. the section I I of the absorber where it absorbs additional refrigerant vapors and collects at the bottom of this section. The absorbent is then pumped by means of the pump 25 through the line 23 into the next section 2'. of the absorber l3 in which the pressure is greater than in the section 6 Because of this greater pressure the partially saturated absorbent which was too warm to absorb further refrigerant vapors in section it under the pressures existing therein absorbs additional refrigerant vapors in the section 2.1.and after passing through the bubble trays 'or other baffling 2'! of this section, collects in a liquid body in the bottom thereof; From this section it is passed through the line 28 by means of the pump 32 to the water cooled cooler 29 and from there through the line 38 into section 3| of the absorber l3. A motor valve 33 in the line 28 is controlled by the liquid level controller 34 maintaining a desired liquid level in the bottom of section 21. V

In section 3| of the absorber i3 the absorbent passes through the bubble trays or otherbaflling 3| into the bottom of this section where itcollects. The pressure in section 3| is higher and the absorbent therefore absorbs additional refrigerant vapors. From this section the absorbent is passed through the line 35 by means of the pump 38 to a water cooler 36 and from there by line 31 into the lowermost section 4| of the absorber l3. As before, a motor valve 39 is included in the line 35 and is controlled by the liquid level controller 40 to maintain a desired liquid level in the lower part of section 3|.

' At :this point it may be noted that for certain 'absorbents and refrigerants the requirement for more efficient-operating conditions may justify cooling the absorbent as it passes through the line 26, by means ofcoolers which may be similar to the heat exchangers and 20. Likewise, as in the case of tray 13, the other sections may be provided with intermediate take-off trays and cooling means similar to the arrangement comprising the parts I9, 20, 2|, 22, 23 and24, or by means of a cold water cooler like that indicated at 29.

The pressure in the absorber section 3| is higher than that in thesection 2'5 and likewise the pressure in section 4| is higher than in the section 3|.

The absorbent discharged into section 4| passes 5 through the bubble tray 4 I or equivalent contact means and collects in the bottom of that section. As the pressure in the sections 21, 3! and 4| is increasingly higher theabsorbent under the same temperature conditions can progressively absorb line 9. The liquid level in the section M is maintained constant by means of the liquid level controller 45 controlling the motor valve 44 in the line 43.

The refrigerant vapors from flash tank 2 pass through line l5 into the highest pressure absorber section 4| and are almost completely absorbed therein. Any impurities in vapors not so absorbed pass through the pipe 18 into the bottom of the next lower pressure absorber section 3i. The maximum pressure in absorber section M is 4 determined through back pressure regulator valve 41 included in the line 46.

The space in the heat exchanger 26' around its tubes is supplied with liquid refrigerant from the flash tank 48 through the line 55 and the refrigerant vapors from that space are returned to the top of thefiashtank 48'throughtheline 56. The refrigerant vapors from flash tank 48 pass through line 49 into absorber section 3| and are therein almost completely absorbed. Any impurities andunabsorbed vapors pass from the top of section 3! into the next lower pressure absorber 21 through pipe 56 in which is the back pressure regulator valve 5!.

Some of the cold liquid refrigerant from flash tank 2 passes through the line 52 into the flash tank 48 and the liquid level therein is maintained by means of the motor valve 53 in the line 52 controlled by the liquid level controller 5i. Thus sufiicient liquid refrigerant flows from flash tank 2 to flashtank 48 to maintain a liquid level thereinsufficient to keep the cooling device of cooler 2|! submerged in liquid refrigerant delivered thereto through the pipe 55.

Cold liquid refrigerant, in this case anhydrous ammonia, flows from the flash tank 48 through the line 5'! intoflash tank 58, in which a constant liquid level is maintained by the operation of motor valve 59 under the control of the liquid level controller 60. The reduction of pressure on the refrigerant as it passes through the valve 59 causes evaporation of the refrigerant to continue until the refrigerant is cooled to its boiling temperature under the existing pressure. The refrigerant vapors formed in the flash tank 58 pass into absorber section 2'! through the line 6|. and are almost completely absorbed therein. Any impurities and unabsorbed vapors pass through pipe 62 into the next lower pressure absorber section The back pressure regulator 63 is included in this line.

The cold refrigerant close to its full coldest temperature passes from the flash tank 58 through the pipe 54 into the heat exchanger 65 where this low temperature refrigerant is employed to cool the material or substance forwhich the system is provided. The cold refrigerant submerges the tubes in the heat exchanger 65 and the material to be refrigerated is delivered to the interior of the tube through the line 68 and removed at the desired temperature through the line 69. The tubes in heat exchanger 65 are held submerged in liquid refrigerant by means of the motor valve 66, the flow in the line 64 being regulated by valve 66 which is controlled by the liquid level controller 61.

The refrigerant vapors formed by the absorption of heat from the material to be refrigerated are delivered by the line 10 into the lowest pressure and therefore the coldest absorber section Any vapors not absorbed in the series of absorbers accumulate in the top of the absorber section II and are discharged through pipe 1| into the air or to some place for further processing. If the pressure in section is sub-atmospheric a suitable compressor or vacuum pump 12 is placed in the line 7| to maintain the desired pressure in section With such a system it is possible to cool the refrigerant to a temperature of from minus 50 to minus degrees F.

If the material to be refrigerated is to be cooled through a considerable range of temperature it may be cooled by means of a series of progressively cooler heat exchangers each supplied with liquid refrigerant from the most suitable of the flash tanks 2, 48 and 58, or from other flash tanks suitably connected in the circuits. The vapors from each cooler pass to that section of the absorber I3 in which the pressure corresponds to the evaporating temperature in the heat exchanger.

For some refrigerants and absorbents it may be desirable to place a compressor in the pipe III so as to either decrease the pressure in the refrigerator B5 or increase the pressure in absorber section I I.

A typical application for a system of this type would be its use to condense ethane in refrigerator 65 under about 70 pounds per square inch. The ethane could then be evaporated at atmos pheric pressure to furnish refrigeration to condense methane at about 500 pounds per square inch to produce the final cooling medium for a denitrogenation plant.

There is disclosed in Figure 2 an application of the principles of this invention wherein natural gasoline is separated from natural gas by refrigeration. Such a system is much more suitable for this purpose than a propane compression, refrigeration and purification cycle, as sometimes used for the purpose. The fire and explosion hazard presented by the use of propane is eliminated by the ammonia absorption system and leaks are more easily located, thereby reducing losses to a minimum. As compared with the propane compression refrigeration system, the ammonia absorption refrigeration system contains very little moving equipment, and such as is employed is relatively inexpensive and is simple to repair and maintain. The advantage of a multi-stage ammonia evaporation refrigeration system is that cooling may be efiected in stages where the ammonia evaporated for highest cooling can be absorbed in the same aqua ammonia used for absorbing the ammonia evaporated for lower temperature cooling.

Prior multi-stage ammonia evaporation refrigeration systems have been devised, In these systems the liquid anhydrous ammonia from the condenser was supplied to each of four evaporators and therefore liquid ammonia was flashed from its initial temperature and pressure to the desired temperature and pressure in each evaporator. This is to be contrasted with the instant system in which the liquid ammonia is flashed from the initial temperature and pressure to a pressure substantially equal to that of the highest pressure absorption stage; the residual liquid ammonia which has been cooled by this flashing operation is then flashed in a second stage to a pressure substantially equal to that of the next lower pressure absorption stage, etc. This process results in the aqua ammonia in each absorption stage being saturated at the pressure in that stage with the result that less aqua ammonia has to be circulated for a given refrigeration load.

Referring to Figure 2, liquid ammonia from a receiver I5 at 90 degrees is expended into a flash tank I8 to a pressure of 30 pounds per square inch absolute. It is delivered to the flash tank through the line I6 containing a motor valve 11 controlled by the liquid level controller on the flash tank I02. This reduction in pressure results in the evaporation of approximately 20% of the ammonia causing a cooling of the remaining refrigerant liquid to a temperature of 0 F. The vapors pass from the flash tank I8 through the line I9 into section 80 of the absorber 580, which section is maintained at a pressure of 30 pounds per square inch absolute. The liquid ammonia at 0 F. passes by line 8I into the first stage 82 of the natural gas cooler. A motor valve 83 is included in line BI and is controlled by the liquid level controller 84. The various heat exchangers of the gas coolers are like those previously described, that is the heat exchanger 5, for example, and the liquid refrigerant at 0 F. passes around the tubes from one heat exchanger to the next in series in the stage 82, as indicated in the drawings. The natural gas is delivered through the line 85 into the branch pipes which connect the various heat exchangers of each stage in series, as indicated in the drawing, so that the final cooled gas ultimately reaches the line I40 after passing through the tubes of the heat exchangers of the three stages 82, 92 and H9 of the gas cooler.

In the first stage 82, the refrigerant is cooled to about minus 20 F., part of the liquid refrigerant evaporating in the heat exchangers of the first stage to thus reduce the temperature of the remainder. The natural gas which is delivered at 2 F. to the first stage is cooled. to about ininus 10 F.

From the first stage 82 of the gas cooler the remaining vapors and liquid ammonia pass into a separator 81 through the line 86, where the vapors and liquids are separated. The vapors from the separator 81 pass through the line 88 into the section 89 of the absorber which is maintained at about 18 pounds per square inch absolute, and the liquid refrigerant from the separator 81 passes through the line 89 into the second stage 92 of the gas cooler. A motor valve is included in the line 89' and is controlled by the liquid level controller 9I on the separator 81. In the second stage coolers part of the liquid refrigerant evaporates to cool the liquid to about minus 30 F. and supplying the refrigeration needed to cool the gas stream from minus 10 F. to about minus 20 F. as they pass through the second stage coolers From the second stage coolers the vapors and liquids pass through the line 93 into a second separator 94. The vapors from this separator at about minus 30 F. pass through the line 95 into the section 91 of the absorber which is maintained at a pressure of about 14 pounds per square inch absolute. The liquid refrigerant at about minus 30 F. which collects in 94 in delivered by the line 98 into the third stage of coolers I'M. A motor valve 89 is included in the line 98 and is controlled by theliquid level controller I00 on the separator 94.

In the coolers IIO part of the liquid refrigerant evaporates to cool the remainder to about minus 45 F. effecting a cooling of the gas from minus 20 F. to about minus 30 F. From the final stage of coolers the vapors of any remaining liquid ammonia pass into a third vapor separator I02 through the line IOI and by-pass lines I60 and NH. From this separatorthe vapors pass through the line I 83 into the remaining section I85 of the absorber 590, wherein a pressure of about 9 pounds per square inch is maintained. A liquid level controller I62 on the separator I82 controls the motor valve II in the line I6 so that the tubes in the gas coolers are kept immersed in liquid ammonia.

The various sections of the absorber 500 contain bubble trays as in the arrangement of Figure 1 to effect eificient contact of the ammonia vapors with the aqua ammonia to insure maximum absorption thereof. Take-01f trays are provided so that the aqua ammonia can be cooled as needed by pumping it through water cooled coolers to remove the heat of absorption as in the case of the arrangement of Figure 1. The last inter= mediatetake-o'ff traysinsection I05 are provided with; liquid removal lines which con'tain the water coolers I06" and Ill! and the pumps as shown. The liquid which collects in the bottom of the section I05 is conducted to the top of section 91 by means of the pump H3. The line including the cooler I88 and the pump removes the liquid from the take-off tray in section 91 and delivers it into that section below the tray. The liquid which collects inthe bottom of section 9'! passes through the water cooler IIIIl and is pumped into the top of section 89 This section has several take-off trays andthe liquid is transferred from above them to below them by means of lines containing the coolers III and III and pumps, as shown. The liquid which collects in the bottom of section 89 is pumped to the top of section BI! by means of the pump H4. Section St has a take-on? tray" from which the liquid passes through the water cooler H2 and a pump to the compartment below this tray.

The separated or strong aqua ammonia is pumped from the bottom of section 80 through the line I II to and through the heat exchangers I F8 and by means of line I26 into the bubble tray evaporator H9. The weak aqua ammonia, practically pure water, at boiling temperature, passes from the bottom of evaporator II9 by gravity through the line I2' I- to the boiler I22-,- The steam from this boiler enters the evaporator H9 below the trays thereof through the line I23. This steam supplies the heat required to distill the ammonia from the aqua ammonia. Practically all of the steam is condensed in the evaporator but about 5% remains in the ammonia vapors passing to the analyzer I24; The weak aqua ammonia which collects in the bottom of evaporator I I9 passes in part to the heat exchangers I I8 where the relatively colder saturated aqua ammoni'a passing through these heat exchangers from line I IT chills the weak aqua ammonia on its way to the top of absorber section I05 through the line H5. Further cooling, if desired is effected in the water cooled cooler H5. A motor valve I50 in this line is controlled by the liquid level controller I-EI so that the desired pressure is maintained in section I05.

In the analyzer I24 the vapors are cooled from about 250 F. to about 110 F. under which condition the quality of the ammonia vapor is increased to about 99.4% and the condensed steam and ammonia solution is returned to the top tray of the evaporator. In order to further dehydrate the ammonia vapors they are passed upward through a fractionator' comprising the section H9 of the evaporator containing a number of bubble trays. Suflicient liquid ammonia is introduced from the ammonia receiver by means of a pump in the line I2! to the top tray of the fractionator so that practically all of it is evaporated in cooling the ammonia vapors down to condensing temperatures. By this arrangement the quality of the anhydrous ammonia can easily be held above 99.9%. The ammonia vapors from the top of the fractionator are delivered through the line [III to the water cooled cooler I32 where they are condensed and returned to the receiver I5, at a temperature of about 90 F.

The top of the absorber 590 is provided with a line I28 and a pump for purging the absorber and aiding in maintaining the desired pressure in section I05 thereof.

The top of the receiver 15 is provided with a bleed line I29 containing the back pressure valve scribed,

82 HO to maintain the necessary-pressure: in the 'receiver- I5: Line |29 may be connected to the bottom of the absorber so that any ammonia; in the vapors-is recovered.

The natural gas and gasoline at about minus 35 F1 are delivered tothe separator I41 through the line I40. The natural gasoline is taken off through the line I42 and the uncondensed gas is withdrawn through: the line I43.

From the above description it will be apparent to those skilled in the: artthat the subject matter of this invention: is capable of some variation indeails, some of which have been indicated, and

I do not, therefore, desire: to be limited to the disclosure but only the claims granted me.

What is claimed is:-

1. A method of refrigeration which comprises, subjecting a stream of liquefied ammonia in several successive stages to a pressure drop to flash a portion thereof at each stage into gaseous ammonia to cool the liquid ammonia remaining at each stage and progressively absorbing the ammonia vapors thus generated with a stream of aqua ammonia in stages of increasing concentration and pressure, whereby the liquid ammonia remaining in the final stage is cooled to a desired temperature and removing the heat of absorption from the aqua ammonia stream prior to each absorption step.

2. A method of refrigeration which comprises successively subjecting a stream of liquefied ammonia to conditions of su'cceedingly lower pressure to flash a portion thereof at each pressure stage into gaseous ammonia, progressively countercurrently absorbing the ammonia vapors thus generated with a stream of aqua ammonia where by the same stream of aqua ammonia absorbs the ammonia vapors generated in said successive stages under conditions of increasing pressure, and removing the heat of absorption from the aqua ammonia stream prior to each absorption step by heat exchange at at least some of said stages with thecooled ammonia at these stages.

3. In a refrigeration system of the type decomprising a plurality of absorption chambera. means for delivering the absorbent successively from one chamber to the next, means for maintaining a different pressure in each of the said chambers, means for supplying the absorbent to the chamber of lowest pressure, means for successively reducing the pressure on a stream of liquefied ammonia to convert a portion thereof into ammonia vapors and cool the remaining portion of liquid ammonia, means for delivering the ammonia vapor generated at the first stage to the chamber of highest pressure, means for delivering the ammonia vapor generated at each of the'succeeding stages to said remaining stages respectively to concentrate the absorbent, and means for removing the heat of absorption from the absorbent during transference from at least one chamber to the succeeding chamber.

4. In a refrigeration system of the type described, comprising a plurality of absorption chambers, means for delivering the absorbent successively from one chamber to the next, means for maintaining a different pressure in each of the said chambers, means for supplying the ab sorbent to the chamber of lowest pressure, means for successively reducing the pressure on a stream of liquefied ammonia to convert a portion thereof into ammonia vapors and cool the remaining portion of liquid ammonia, means for delivering the ammonia vapor generated at the first stage to the chamber of highest pressure, and means for delivering the ammonia vapor generated at each of the succeeding stages to said remaining stages respectively to concentrate the absorbent, and means for removing the heat of absorption during transference from at least one chamber to the succeeding chamber by heat exchange with the ammonia cooled at one of said stages.

5. In a refrigeration system, the combination comprising a source of liquefied anhydrous ammonia, means for progressively reducing the pressure on the body of said liquefied ammonia in successive stages, and means for progressively absorbing gaseous ammonia formed at each pressure reduction with aqua ammonia in successive stages of increasing pressure, the aqua ammonia increasing in concentration at each of said stages, means for maintaining the aqua ammonia at each succeeding absorption stage under a predetermined pressure, and means for cooling the aqua ammonia after each absorption step and prior to its introduction to the next step.

6. In a refrigeration system of the type described, the combination comprising a source of weak aqua ammonia absorbent, a source of liquid anhydrous ammonia, means for successively expanding the body of the said liquid ammonia in indirect heat exchange with said aqua ammonia absorbent in several stages to cool both the aqua ammonia and the liquid ammonia, said absorbent being that which is to be used in the succeeding stage of absorption, a plurality of absorption chambers maintained at progressively increasing pressures, means for contacting the vaporized ammonia and the aqua ammonia in said chambers to increase the concentration of the aqua ammonia in each of said stages, and

means for maintaining pressures in said chambers substantially equal to the ammonia vapor pressures at said respective stages.

7. In a refrigeration system of the type described, the combination comprising a source of aqua ammonia, a source of liquid anhydrous am monia to form a body thereof, means for successively flashing vapor from the body of liquid ammonia retained in indirect heat exchange relation with said aqua ammonia in several stages through reduction in pressure on the body of liquid anhydrous ammonia in each successive stage, thereby cooling both the aqua ammonia and the liquid ammonia, a plurality of absorption chambers maintained at successively higher pressures and means for conducting the ammonia vapors resulting from evaporation of said anhydrous ammonia together with the aqua ammonia through said absorption chambers to absorb' the ammonia vapors successively under pressures substantially equal to the respective pressures under which they are evaporated.

FORREST E. GILMORE.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 967,992 Starr Aug 23, 1910 2,182,453 Sellew Dec. 5, 1939 2,326,900 Thomas Aug. 17, 1943 FOREIGN PATENTS Number Country Date 579,992 Germany July 4, 1933 

1. A METHOD OF REFRIGERATION WHICH COMPRISES, SUBJECTING A STREAM OF LIQUEFIED AMMONIA IN SEVERAL SUCCESSIVE STAGES TO A PRESSURE DROP TO FLASH A PORTION THEREOF AT EACH STAGE INTO GASEOUS AMMONIA TO COOL THE LIQUID AMMONIA REMAINING AT EACH STAGE AND PROGRESSIVELY ABSORBING THE AMMONIA VAPORS THUS GENERATED WITH A STREAM OF AQUA AMMONIA IN STAGES OF INCREASING CONCENTRATION AND PRESSURE, WHEREBY THE LIQUID AMMONIA REMAINING IN THE FINAL STAGE IS COOLED TO A DESIRED TEMPERATURE AND REMOVING THE HEAT OF ABSORPTION FROM THE AQUA AMMONIA STREAM PRIOR TO EACH ABSORPTION STEP. 